Hi
Few weeks ago I have noticed that Android projects created by XS on Mac cannot be opened with VS 2010 and 2012. Recently this is true for XS on Windows too.
From what I have found all Android projects now have 3 GUIDs in ProjectTypeGuids xml element in csproj file.
- VisualStudio
{10368E6C-D01B-4462-8E8B-01FC667A7035};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC} XamarinStudio
{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}find . -name "*proj" | xargs grep "ProjectTypeGuid" > ProjectTypeGuids.txt
Excerpt
./VisualStudio/2012/CS/Android/AndroidApplication-CS/AndroidApplication-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./VisualStudio/2012/CS/Android/AndroidBindingLibrary-CS/AndroidBindingLibrary-CS.csproj:
<ProjectTypeGuids>{10368E6C-D01B-4462-8E8B-01FC667A7035};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./VisualStudio/2012/CS/Android/AndroidClassLibrary-CS/AndroidClassLibrary-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./VisualStudio/2012/CS/Android/AndroidHoneycombApplication-CS/AndroidHoneycombApplication-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./VisualStudio/2012/CS/Android/AndroidIceCreamSandwichApplication-CS/AndroidIceCreamSandwichApplication-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./VisualStudio/2012/CS/Android/AndroidOpenGLApplication-CS/AndroidOpenGLApplication-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./XamarinStudio/Mac/CS/Android/AndroidApplication-CS/AndroidApplication-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./XamarinStudio/Mac/CS/Android/AndroidHoneycombApplication-CS/AndroidHoneycombApplication-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./XamarinStudio/Mac/CS/Android/AndroidIceCreamSandwichApplication-CS/AndroidIceCreamSandwichApplication-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./XamarinStudio/Mac/CS/Android/AndroidJavaBindingLibrary-CS/AndroidJavaBindingLibrary-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{10368E6C-D01B-4462-8E8B-01FC667A7035};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./XamarinStudio/Mac/CS/Android/AndroidLibraryProject-CS/AndroidLibraryProject-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./XamarinStudio/Mac/CS/Android/AndroidOpenGLApplication-CS/AndroidOpenGLApplication-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./XamarinStudio/Mac/CS/Android/AndroidUnitTestProject/AndroidUnitTestProject.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./XamarinStudio/Windows/CS/Android/AndroidApplication-CS/AndroidApplication-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./XamarinStudio/Windows/CS/Android/AndroidApplication-CS/AndroidHoneycombApplication-CS/AndroidHoneycombApplication-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./XamarinStudio/Windows/CS/Android/AndroidApplication-CS/AndroidIceCreamSandwichApplication-CS/AndroidIceCreamSandwichApplication-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./XamarinStudio/Windows/CS/Android/AndroidApplication-CS/AndroidJavaBindingsLibrary-CS/AndroidJavaBindingsLibrary-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{10368E6C-D01B-4462-8E8B-01FC667A7035};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./XamarinStudio/Windows/CS/Android/AndroidApplication-CS/AndroidLibraryProject-CS/AndroidLibraryProject-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./XamarinStudio/Windows/CS/Android/AndroidApplication-CS/AndroidOpenGLApplication-CS/AndroidOpenGLApplication-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
./XamarinStudio/Windows/CS/Android/AndroidUnitTestProject-CS/AndroidUnitTestProject-CS.csproj:
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{F278D4AB-4730-4720-B08E-FE5E31564D9E};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>